But, in the end, the ballyhooed investigation produced more confusion than clarity.

The only public court case to emerge from the probe drew to a close here last week in a mistrial. The jury couldn't reach a verdict on whether a single $500 bribe paid by Dale Brown, a small Texas contractor, was illegal.

Yet the reverberations from the bizarre case are far from over. Lawsuits and bitter accusations, ranging from a political coverup to entrapment, are still flying in a case that has been closely watched in government and business circles. It has set two proud agencies - the FBI and NASA - against each other, sullied the images of top federal officials, and drawn plenty of conspiracy buffs.

''You don't spend more than $2 million to go after some penny-ante guys like Dale Brown and [his boss Leonard Neal] Jackson for a $500 bribe,'' says John Crenshaw, a San Antonio consultant who became ensnared in the operation but was never indicted. ''An awful lot of information had to be withheld.''

No top officials charged

The probe did produce plea-bargain convictions against two mid-level NASA employees, 10 contractors, and two firms. Maryland-based Martin Marietta Corp. made a $1 million out-of-court settlement payment.

But FBI agent Hal Francis, the central figure in the sting operation, has repeatedly told reporters the past two years that ''the big ones got away.'' Agent Francis, who posed as a wealthy Atlanta investor, said Mr. Brown should never have been tried. Francis added in a recent interview that ''at least 25, and as many as 50, cases of improper conduct were uncovered by the probe, but were stymied by prosecutors.''

But assistant US Attorney Abe Martinez rejects suggestions that there was a coverup. ''The reason the undercover operation was instituted was that contractors were committing crimes,'' Mr. Martinez says. ''This investigation only got small fish because it was only after those small fish.''

The probe was launched almost four years ago when NASA's Inspector General's office handed the FBI more than 300 complaints - many received anonymously - alleging bribery and mismanagement by NASA officials and contractors. The focus, according to Francis, was on the Life Sciences division at the Johnson Space Center, its director Carolyn Huntoon, now the head of the Johnson Space Center, and the contracting firm General Electric Government Services.

But top NASA officials or contractors were never indicted. As a result, cries of cover-up were lodged against the FBI. Such suspicions were given weight when a 1994 GAO investigation, ordered by Sen. John Glenn, determined that former NASA Inspector General Bill Colvin had tipped off a colleague about the FBI's undercover probe. Colvin resigned his post in September 1994.

Suspicions were furthered when Martin Marietta, which purchased General Electric Government Services in 1993, paid a $1 million ''settlement payment.''

Claims of set ups

Many of the men targeted in the FBI sting maintain they were set up. They tell of being pressured into making a bribe after their disguised government suitors spent thousands of dollars on such things as Florida fishing vacations and parties to gain their trust.

David Proctor, a former engineer at NASA's Life Sciences Division now serving five months in prison for bribery, recalls being taken to a Houston warehouse, showed large photographs and placards displaying the maximum penalties for the crimes he was told he had committed. Proctor, who admits to helping write a NASA contract proposal during off-duty hours, says FBI agents held a gun to his head while he was warned not to get a lawyer, or talk to the press.

Proctor says he was forced to go undercover for the FBI for three months during 1993 recording conversations with NASA officials and contractors. But even after making tapes that he says ''incriminate'' top NASA officials, the FBI refused to follow-up on his leads, or release recorded conversations.

''In the end, they went after some they knew they could charge, and backed off from others who were never meant to be prosecuted,'' Proctor says, who was subpoenaed by Dick DeGuerin, Brown's lawyer, but was not allowed to testify. ''Lightning Strike was selective prosecution,'' he says. ''The big people were protected. It was a cover-up.''

Although little proof is offered, some here fear the FBI probe is being used to tarnish the Johnson Space Center's reputation, thereby prompting cuts in NASA's budget or the transfer of operations to the Marshall Space Center in Huntsville, Ala.

And while Congressional hearings on Lightning Strike have never been held, criticism of the sting led to an investigation by the Justice Department's Office of Professional Responsibility. The internal probe issued a clean report. Jeff Carr, a NASA spokesman, says the investigation demonstrates the space agency willingness to investigate its own workforce and contractors.

The Justice Department intends to bring Brown to trial again in September. A class-action suit is planned against the FBI for abusive conduct.